Impact driven survey monuments made of various materials, such as aluminum, aluminum alloys, or stainless steel, are widely used. These monuments vary in length depending upon the particular characteristics of the ground in which they are used. In some areas requiring relatively deep penetration, sectionalized driven rod monuments, such as disclosed in the patents to Feldman et al, U.S. Pat. No. 4,254,597, and Berntsen, U.S. Pat. No. 4,087,945, are necessary. The sectionalized rods disclosed in these two patents both rotate the rod sections as the monument is driven into the ground to maintain a tight connection between the rod sections and a threaded connector used to interconnect adjacent sections.
Another sectionalized rod monument in which the sections are threaded together is disclosed in the patent to Baumeister, U.S. Pat. No. 3,378,967. The Baumeister device, however, does not include any provision for rotating the sections relative to one another to maintain the threaded interconnection tight as the monument is driven into the ground.
Other types of monuments which are adapted to be buried in the ground in a hole which then is backfilled around the monument also exist. Such monuments range in variety and style from cylindrical tubular monuments, concrete posts, cast iron monuments, cast aluminum, and other types. Many of these prior art monuments are unnecessarily heavy and cumbersome. In addition, many of the prior art monuments are expensive to manufacture and install, which makes them undesirable for wide scale use.
Whenever a maker is used in a location having a relatively high public density, the marker is prone to premature removal or vandalism. Furthermore, markers often are struck by bulldozers, plows, or other equipment operating in the area of the marker. Whether the marker is struck by a bulldozer or is vandalized, the result usually is to bend or move the marker or to totally remove it. This makes it unclear where the original exact survey point marked by the marker is located. If the marker is easy to remove and relocate, it obviously fails to provide the reliability of information concerning the survey point which is intended by the original placement of the marker.
To overcome the problem of movement or removal of markers, various types of break-away monuments have been developed. Monuments of this nature which are typical of the prior art are disclosed in the patents to Berntsen, U.S. Pat. No. 3,748,795, Johnson, U.S. Pat. No. 3,685,237, and Johnson, U.S. Pat. No. 3,899,856. The monument disclosed in the Berntsen '795 patent is a relatively bulky casting of an aluminum alloy having a magnet placed in it near the base and having two intersecting undulating webs connecting the top and base flanges of the monument. At intervals throughout the vertical length of the monument, the webs have transverse lines of weaknesses formed in them. Thus, if the monument is struck at its upper end, the lines of weaknesses are such that the monument will break off at one of these weakness lines to maintain the base in an undisturbed condition, even though the upper part of the monument is moved or totally removed. The magnet which remains attached to the base then facilitates location of the survey point identified by the marker. Even though the marker is made of an aluminum alloy, it is relatively heavy, it requires the digging of a hole prior to its placement, and it is bulky.
The Johnson U.S. Pat. No. 3,685,237, illustrates another prior art construction for a breakaway-type of monument construction. The marker disclosed in this patent is cast iron in the shape of alternate orthoginal thin plates. These plates are designed to fracture whenever transverse external forces are applied to the upper part of the marker. The intent is that at least the lower portion of the marker will remain in place at the survey point for subsequent location. As with the Berntsen marker, it is necessary first to dig a hole in the ground to bury the marker in its installation. Although this type of installation is utilized in many locations, it is a cumbersome one. In addition, because the marker is made from a casting, the manufacturing process necessarily is more expensive than a marker formed from a tube or a rod. Also, since the maker is made of cast iron, it is relatively heavy which further limits the locations in which the marker may be employed and creates additional expenses in transporting of the marker from its place of manufacture and from place to place for installation.
The marker disclosed in the Johnson U.S. Pat. No. 3,899,856, is designed to be driven into the ground; so that it is not subject to the disadvantages of the above-mentioned Berntsen '795 and Johnson '237 markers requiring the digging of holes. The marker of the Johnson '856 patent, however, still is made of two intersecting planar cast iron sections; so that it is relatively heavy and bulky. In addition, it requires a casting process for its manufacture. The marker has a number of slots or fracture zones formed at spaced intervals along its length and is made of brittle cast iron; so that it will crack-off or break at one of these fracture zones whenever the upper end of the marker is subjected to a strong transverse force. In this respect, its function is similar to the breakaway function disclosed in the Bernsten U.S. Pat. No. 3,748,795, and the Johnson Pat. No. 3,685,237.
It is desirable to provide a breakaway or detachable monument which overcomes the disadvantages of the various prior art structures discussed above, and which is simple to install.